Apparatus, method and system of liquid-based, wide range, fast response temperature control of electronic device

ABSTRACT

An active temperature control system for a DUT utilizes a heat sink containing HFE7100 liquid and an electric heater. The liquid is cooled below the set point and the heater is used to bring the DUT up to the set point. Set points in the range of −10 degrees C. to +110 degrees C. can be achieved. The heat sink utilizes only a single coolant for all of the set points, allowing set points to be changed within a few minutes. At a given set point, the heater provides a quick response to offset the effect of self-heating and keep the set point deviation to within a few degrees C. Power following techniques can be utilized to achieve the quick response.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority of, and hereby incorporates byreference as if fully set forth herein, previously filed provisionalapplication No. 60/092,715, filed on Jul. 14, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to temperature control systems which maintain thetemperature of an electronic device near a given set pointtemperature(s) while the device is being operated or tested. Twospecific examples of electronic devices which need to be operated ortested at a constant temperature are packaged integrated chips andunpackaged bare chips.

2. Description of the Related Art

Maintaining the chip temperature near a given set point is not difficultif the power dissipation of the chip is constant or varies in a smallrange while operating or testing. In such cases, it is only necessary tocouple the chip through a fixed thermal resistance to a thermal masswhich is at a fixed temperature. But if the instantaneous powerdissipation of the chip varies up and down in a wide range whileoperating or testing, then maintaining the chip temperature near aconstant set point is very difficult. When chips are being debugged ortested, it is advantageous to evaluate their performance at a variety oftemperatures, ranging from cold to hot. Combining the ability to forcetemperature across a wide temperature range, while accommodating thetemperature changes associated with varying instantaneous powerdissipation, is very challenging.

Typical approaches to solve this problem involve forced air convectionsystems that extend well beyond the desired forcing temperature range atboth the hot and cold ends. In this way, an attempt can be made toaccelerate the chip's temperature conditioning by overcooling oroverheating. As the nominal power density of the chips continue toincrease, the ability of forced air convection systems to overcoolreaches practical limits, causing increases in the temperature errorbetween the desired and actual temperatures relative to set point.Another problem is that chips fabricated in the latest processes have anincreased sensitivity to high temperatures. The potential for chipdamage due to overheating adds risk to the use of the overheatingapproach. Increased time to set point is the result, with lostutilization of expensive test equipment and engineering personnel as anexpense.

Another approach is the use of dual liquid conduction systems, with onehot and one cold liquid. The proportion of the liquids are mechanicallymetered to affect the desired forcing temperature. To achieve fastresponse times, this approach requires that the metering occur veryclose to the chip. This imposes mechanical packaging constraints whichlimit the flexibility to bring the surface of the temperature forcingsystem control surface into contact with the chip or chip package. Evenso, the mechanical metering of the dual liquids is much slower to affecta change in the forcing temperature when compared to the temperaturechanges induced by the chip's instantaneous power dissipation. This alsocauses increased error between the desired and actual temperatures.

The present invention is directed to overcoming or at least reducing theeffects of one or more of the problems set out above.

SUMMARY OF THE INVENTION

This invention combines the optimal liquid and liquid temperaturecontrol system with a heat exchanger. A single liquid is used to coveras much of the temperature range as possible. Modes of the control ofthe heating element are then used to extend the set point temperaturerange which the temperature forcing system contact surface can apply. Inone embodiment of the invention, the flow rate of the liquid through theheat exchanger is metered, to optimize the power dissipation of the heatexchanger, versus the desired thermal control performance at the chip.

The present invention provides a liquid based, wide range, fast responsechip temperature control system. The wide temperature range is achievedby extending the effective temperature range of a liquid based coolantloop with resistive heating in the control surface. In this way, thedesired temperature range for testing chips can be achieved, whilesupplying the features of: (i) fast set point temperature change, (ii)response to instantaneous power dissipation changes, and (iii) smallform factor and flexibility in chip situations.

This system may include: (i) the liquid cooling and recirculationsystem, (ii) the thermal control circuit which controls the heatertemperature, (iii) the algorithms contained in the thermal controlcircuit which perform the translation from a desired device temperatureto a heater control, and (iv) the heat exchanger consisting of a liquidcooled heat sink and a resistive heater bonded to it, which contacts thechip.

Briefly, there is provided according to one embodiment of the presentinvention an apparatus for controlling a temperature of a device. Theapparatus includes a heater, a heat sink, and a temperature controlsystem. The temperature control system is adapted to move thetemperature of the point on the heater from approximately a first setpoint temperature to approximately a second set point temperature.

Briefly, there is provided according to another embodiment of thepresent invention an apparatus for controlling a temperature of adevice. The apparatus includes a heater, a heat sink, and a temperaturecontrol system. The temperature control system is adapted to move thetemperature of the point on the device from approximately a first setpoint temperature to approximately a second set point temperature.

Briefly, there is provided according to another embodiment of thepresent invention an apparatus for controlling a temperature of adevice. The apparatus includes a heater, a heat transfer unit, and atemperature control system. The temperature control system is adapted tomove the temperature of the point on the device by at least 50 degreesC. by controlling power sent to the heater and by controlling atemperature of a surface of the heat transfer unit.

Briefly, there is provided according to another embodiment of thepresent invention an apparatus for controlling a temperature of adevice. The apparatus includes a heater, a heat sink, and a temperaturecontrol system. The temperature control system is coupled to both theheater and the heat sink and is adapted to maintain a temperature of apoint on the device at or near a set point temperature despite theexistence of self-heating of the device.

Briefly, there is provided according to another embodiment of thepresent invention an apparatus for controlling a temperature of asemiconductor device during testing. The apparatus includes a heatexchanger and a temperature control system. The heat exchanger isadapted to be thermally coupled to the semiconductor device duringtesting. The temperature control system is coupled to the heat exchangerand is for controlling the heat exchanger. The temperature controlsystem is adapted to maintain the temperature of the semiconductordevice at or near a set point temperature during testing despiteself-heating of the semiconductor device. The set point temperature canbe set to a first value or to a second value which is at least 25degrees Celsius lower.

Briefly, there is provided according to another embodiment of thepresent invention a method of controlling a temperature of asemiconductor device during testing. The method includes moving thetemperature of the device to approximately a first set pointtemperature. The method further includes moving the temperature of thedevice to approximately a second set point temperature.

Briefly, there is provided according to another embodiment of thepresent invention an apparatus for controlling a temperature of asemiconductor device. The apparatus includes a heat exchanger, a gasinjection fitting, and a temperature control system. The gas injectionfitting is for injecting a gas into a contact region between the heatexchanger and the semiconductor device when the semiconductor device iscontacting the heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a general diagram of the system.

FIG. 2 illustrates a schematic for a liquid coolant system, according toone embodiment of the present invention.

FIG. 3 illustrates a high level schematic of the control electronics forone thermal control channel.

FIG. 4 illustrates a system changing the set point temperature of a testdevice, using the fast set point temperature change feature.

FIG. 5 shows an example profile setup screen.

FIG. 6 illustrates a three channel thermal control subsystem.

FIG. 7 depicts multiple heat exchangers on a multi-chip module.

FIG. 8 contains a graph illustrating temperature control accuracy vs.set point.

FIG. 9 contains a graph showing junction temperature vs. setpoint-to-liquid delta T.

FIG. 10 depicts a heat exchanger with optional conductive coatings orstructures.

FIG. 11 shows a socket assembly plumbed for helium injection.

FIG. 12 contains a graph showing junction temperature vs. time.

FIG. 13 is a high-level block diagram showing an interrelationshipbetween a test control system, a temperature control system, and a DUT.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

1. System Overview

FIG. 1 shows a general diagram of a system 10 according to the presentinvention. As shown, the user operates the system 10 at the operatorinterface panel 12. The operator interface panel 12 serves as aninterface to the system controller 14. The system controller 14 ishoused in the system electronics enclosure 16 and controls the heatexchanger 20 and the liquid cooling and recirculation system 22. Thesystem electronics enclosure 16 also contains the thermal controlchassis 11 immediately under the system controller 14. The two thinmodules below the thermal control chassis 11 are high voltage powersupplies 13, although one embodiment uses one large one instead of twosmall ones. The bottom module is the low voltage power supply 15.

The heat exchanger 20 preferably includes a heater and a heat sink.Other heat exchangers are possible, however. The heat sink preferablycontains a chamber through which the liquid is pumped. Other heat sinksare also possible. Heat sinks, or heat sink systems, with no liquid arealso viable if the thermal conductivity is high enough. In particular,solid heat sinks such as Peltier devices are known in the art which useelectrical signals through the material to control temperature andtemperature gradients. A heat sink may also equivalently be referred toas a heat transfer unit, thus focusing attention on the fact that theheat sink may also act as a heat source.

The heater of the preferred embodiment is a resistive heater. However,it is to be understood that many other types of heaters can also beused, including without limitation a heater utilizing lasers, otheroptics, or electromagnetic waves.

It is also to be understood that a typical heater, or heat sink, willhave a temperature gradient across the surface. In the case of a heater,the existence of a gradient is due, in part, to the fact that theheating element usually occupies only a portion of the heater.

The liquid cooling and recirculation system 22 supplies a liquid to theheat exchanger 20, specifically to the heat sink, through the boom arm18. The boom arm 18 also carries the control signals from the systemcontroller 14 and the thermal control chassis 11 to the heater.

A test head 21 is adapted to be positioned under the heat exchanger 20.The test head 21 preferably contains a test socket which is used formating with a device under test (“DUT”) such as a chip.

FIG. 2 shows a general schematic 23 for a coolant system which may beused with the present invention. The block diagram of a chiller system22 may be used for implementing the liquid cooling and recirculationsystem 22 of FIG. 1. The chiller system 22 pumps the liquid through afilter 26, a flow control 28, a flow sensor 30, and finally to the heatexchanger 20. The liquid then returns to the chiller system 22 to becooled and pumped back through the system. In the embodiment shown inFIG. 1, both the forward and return paths for the liquid go through theboom arm 18 (of FIG. 1).

FIG. 10 shows, among other things, an embodiment in which a heatexchanger 20 is attached to a DUT 104. The heat exchanger 20 comprises aheater 112, a heat sink 108, heater power and heater RTD lines 102, andliquid coolant lines 110. The heater 112 is flush against a surface ofthe heat sink 108 which is attached to a heat sink 108. The liquidcoolant lines 110 supply liquid to the liquid heat sink 108. The lines102 supply power to the heater 112. The device 104 whose temperature isto be controlled is disposed beneath and in contact with a bottomsurface of the heater 112.

FIG. 10 also shows optional conductive coatings and structures 106 whichmay be placed on the heater 112 to improve the thermal conductance tothe chip 104. This approach improves the thermal conductance between theheater 112 and the chip 104 when compared to a trapped layer of air.Improving this thermal conductance then improves the chip temperaturecontrol performance. For a given power envelope of a DUT, the improvedthermal conductance lowers a required temperature difference between aheat sink and a set point, as more fully explained later.

Optionally, the socket assemblies used to receive the chip are plumbedto allow for helium gas to be injected. This allows for helium todisplace the air between the heater and the chip. Helium is morethermally conductive than air, improving the thermal controlperformance. FIG. 11 illustrates an embodiment of a socket assemblyplumbed for Helium injection. The helium flow can be controlled in avariety of ways known to one of ordinary skill in the art. Oneembodiment is for a control system to control the flow during actualtesting of a device.

FIG. 7 illustrates an alternative embodiment in which multiple heatexchangers are utilized. Referring to FIG. 7, heat exchanger 54 and heatexchanger 56 have separate inlets and outlets 58, 60. This allows thetwo heat exchangers to be separately controlled and maintained atseparate temperatures, if desired, using a single chiller (see FIG. 2,element 22) and separate flow control for each heat exchanger (see FIG.2, elements 28 and 30). Preferably, each sub-system includes separateheaters attached to the separate heat sinks in the manner illustrated inFIG. 10. In such an embodiment, the heaters are each controlledseparately. There are also embodiments that allow two separate heatersto be controlled by a single thermal control channel.

Alternatively, the separate inlets and outlets 58, 60 are connected tothe same coolant system and the two heat exchangers 54, 56 operated withliquid coolant which is at the same temperature in each heat exchanger.With separate heaters attached to the heat exchangers the separate diesmay still be operated at different temperatures.

In yet a further alternative, a single coolant system is used formultiple DUTs, such as a multi-chip module 61, and the multi-die heatexchanger 56 is utilized. The multi-die heat exchanger 56 can haveseparate heaters interposed between it and the respective DUTs of themulti-chip module 61.

In yet a further alternative, a single coolant system is used formultiple heat exchangers, and in-line heaters are installed in thecoolant supply line (between elements 30 and 20 of FIG. 2) to raise thetemperature of the coolant being supplied to one or more heat exchangersseparately, to further increase the temperature control capability.

Separate control is accomplished by expanding the number of controlloops. This can be achieved by adding additional instances of thethermal control circuitry to the system. This enables the thermalcontrol of individual chips of a multi-chip module. FIG. 6 illustratesan embodiment of a thermal control chassis 51, capable of housingthermal control boards 52 for three control loops. FIG. 6 contains apicture of a three channel thermal control sub-system 50. The system 50includes a chassis 51 which includes three thermal control boards 52,safety relays 59 (which are part of the self-test functionality in theelectronics enclosure 16 and are used to test the integrity of theheater and RTD traces), three power monitoring circuit boards 55, andthree power amplifiers 57. FIG. 6 shows various other components,including system connectors 53, which are standard for a chassis housingelectronic equipment.

FIG. 3 shows a high level schematic 46 of the control electronics for athermal control channel such as a thermal control board 52 of FIG. 6.The schematic 46 can be applied to the control of a heater in a heatexchanger 20. The general operation of the schematic 46 is describedbelow, and details of this schematic for a particular embodiment can befound in an application by Jones which is discussed in a later sectionof this disclosure.

Briefly, in one embodiment, the power monitoring circuit 34 of FIG. 3monitors the power used by a chip (not shown) and supplies an indicationof that power to the thermal control board 36. The thermal controlcircuit 38 accepts this input. The thermal control circuit 38 alsoaccepts as an input the temperature of a forcing system, which is, forexample, the temperature of the heater surface (not shown) which is incontact with the chip. The thermal control circuit 38 then computes athermal control signal which is sent to the heat exchanger temperaturecontrol 40. The heat exchanger temperature control 40 determines aheater power signal and sends it to a power amplifier 42 which in turnsends a heat exchanger power signal to the heat exchanger 20. In thisembodiment, the thermal control board 36 computes a signal that controlsa heater, which is part of the heat exchanger 20.

As stated earlier in the description of FIG. 1, the heat exchanger 20preferably includes a heat sink which contains a chamber through which aliquid is pumped. Ideally, the liquid in the heat sink must: (i) have alow and relatively flat viscosity over the required temperature range sothat it can be pumped; (ii) have a thermal capacity which is high enoughover the required temperature range so that it can serve as an efficientheat exchange medium; (iii) be a safe chemical so that no injuries willresult if any part of the human body is exposed to the liquid; and (iv)be a dielectric, meaning that the liquid will not electrically short anycircuit onto which it might be spilled. Ideally, the minimum temperaturerange for the first of these two characteristics extends fromapproximately 40 or 60 degrees C. down to approximately −40 degrees C.

It has been determined that a liquid (HFE7100) meets all of the aboverequirements. HFE7100 is a specialty liquid manufactured by 3Mcorporation. HFE7100 contains ethyl nonafluorobutylether and ethylnonafluoroisobutylether. Preferably, HFE7100 is used at normal strength.HFE7100 is non-toxic, non-explosive, non-conductive electrically, and isa safe liquid as compared to other alternatives. As an alternative,water can be used with additives, such as methanol or ethylene glycol.However, such a mixture is potentially explosive, poisonous, and has ahigh viscosity at low temperatures. Further, it is difficult to achieveset points below 15 degrees C. with such water based liquids.Additionally, it is difficult to maintain set points below roughly 60degrees C. for devices which self-heat (see above discussion of FIG. 8).

The HFE7100 liquid meets the requirements for a minimum temperaturerange of from approximately −40 degrees C. to approximately +40 or +60degrees C. The liquid boils at roughly 60 degrees C. Other liquids,without similar thermal, physical, environmental, and dielectricproperties, are typically only operable in a more restricted range, forexample at low temperatures or at high temperatures but not both.Therefore, a heat sink chamber would have to be drained and flushed andthen filled with a different liquid mixture for operating at differenttemperatures. HFE7100, however, can typically be used for set points, asdifferentiated from the liquid temperature, in an approximate range of−10 to +110 degrees C. Further, the limits on the temperature range ofHFE7100 can be extended in both directions with different chillers.Other products, including new HFE products by 3M, which have similarthermal, physical, environmental, and dielectric properties, can serveas alternatives to HFE7100. Other alternatives may exist or may beintroduced into the market-place that allow the temperature range to beextended even further (similar heat capacity and viscosity at lowercoolant temperatures to achieve lower setpoints, and/or a higher boilingpoint to achieve higher setpoints).

One embodiment uses a chiller which is not pressurized and which canonly bring the liquid down to −40 degrees C. An alternate chiller couldcool the liquid further and/or pressurize the liquid to allow it to beheated further as well. The current temperature range of the chiller issufficient to achieve the desired set points when operated with a heaterwhich can maintain a temperature differential of roughly 90 degrees C.One embodiment uses such a heater.

A preferred chiller can bring the temperature of the liquid from −40degrees C. up to +40 degrees C. in about five minutes. This timeincreases as the amount of coolant increases and as the thermal mass ofthe coolant system and the plumbing increases. Thus, larger systems willtake longer to move the temperature of the coolant.

An embodiment uses a vacuum at the return side to produce a negativepressure coolant loop. Such an embodiment has better leak tolerance inthat it accumulates air in the system instead of spraying liquid fromthe system. Preferably the system is built with quick disconnectcapability, thus precluding the possibility of welding the system andvirtually eliminating leaks. Embodiments may also use a slightlypositive pressure to increase the flow rate. Such positive pressures,however, do not significantly affect the boiling point of the liquid.

2. System Operation

The preferred embodiment controls the temperature of a device 104 usinga liquid-based heat sink 108 coupled to a heater 112, as shown in FIG.10. The fluid, in the liquid coolant lines 110, cooling the heat sink108 is typically kept at a roughly constant temperature below the setpoint while the heater 112 is used to bring the device temperature up tothe set point. Thus, the coolant and the heater 112 are operated atdifferent temperatures. The heater 112 is further used to effect quickchanges in temperature control to accommodate and compensate for quickchanges in the device 104 due to self-heating, for example. Manytechniques can be used to accomplish the necessary active control of theheat exchanger 20.

A. Control System

Co-pending patent application U.S. Ser. No. 08/734,212 to Pelissier,filed on Oct. 21, 1996, and assigned to the present assignee, andpreviously filed provisional application No. 60/092,720 to Jones, etal., assigned to the present assignee, filed on Jul. 14, 1998, are bothhereby incorporated by reference as if fully set forth herein. Pelissierand Jones describe using power usage of an electronic device under testto control the temperature of the electronic device. Such methods may beused to accomplish or assist in the control of the temperature using thepresent invention. Additionally, temperature following methods, or anyother type of active temperature control, may also be used with thepreferred embodiment of the present invention.

Referring to FIG. 3, the thermal control board 36 performs a variety offunctions. Generally speaking, a thermal control board must processinput information related to the device temperature, and then determinehow to adjust the heat exchanger to maintain the DUT at the desired setpoint. Such information can include without limitation the actualtemperature of the DUT, the power consumed by the DUT, the currentconsumed by the DUT, the ‘predicted’ power of the DUT in a Feed Forwardarrangement, or an indicator of the DUT temperature. A power profile,created for a particular device, can also be used as an input which isrelated to the temperature of the particular device. The use of powerprofiles is described, for example, in the Pelissier and Jonesapplications mentioned earlier. Indicators of the temperature can bederived from a thermal structure such as, for example, thermal diodes orresistors in the DUT. Note that the input information related to thedevice temperature may have information related to the absolute orrelative position, velocity, and/or acceleration of the actual chiptemperature. A thermal control board may be implemented in a variety ofmethods, including analog or digital circuitry as well as software. Thisapplies both to the processing operations associated with accepting theinputs and making the necessary calculations, as well as to the controlof the heat exchanger temperature. A variety of control techniques mayalso be used to achieve a controller with a desired combination ofproportional, integral, and/or derivative control features.

The control of the heater is the principal task of the temperaturecontrol system. The fluid in the heat sink must also be controlled bysetting the temperature and the flow rate of the liquid. These settings,however, do not typically need to be changed during a test at a givenset point and many different settings are possible. Typical applicationsoften use a flow rate of 0.5-2.5 liter/min, but this is largely afunction of the heat exchanger design for the application. This range offlow rates is often varied across the temperature range, with a higherflow rate being used with higher liquid temperatures and a lower flowrate being necessary for lower liquid temperatures due to the typicallyhigher viscosity. It should also be clear that lower flow rates are onefactor that can allow a higher delta T value. Where appropriate, thisdisclosure describes the settings used or the factors involved inselecting those settings.

The control requirements can be sharply reduced in applications which donot require active control. Passive applications, where self-heating isnot occurring or where it is not being actively offset, do not requirethat a temperature control system react as quickly. Burn-in is anotherexample of an application which often does not need active temperaturecontrol, because the functional tests which are run often do notdissipate enough power to induce self-heating.

B. Heat Sink Liquids

As previously mentioned, a heat sink is preferably kept at a relativelyconstant temperature below a set point temperature. The heat sinkpreferably has HFE7100, described earlier, flowing through a chamber.

FIG. 8 contains three curves which show the set point deviation as afunction of set point temperature for three different systems. Onesystem uses a water/methanol mixture of 40% water and 60% methanol asthe heat sink liquid and uses direct temperature following as thecontrol method. A second system also uses the same water/methanolmixture, but uses power following as the control method. A third systemuses HFE7100 along with power following. The systems are attempting tocontrol the temperature of a device under test. The DUT has a powerusage which is rapidly changing between 0 and 25 watts/square cm.

The curves show that the water/methanol mixture begins to have problemsat set points around 60 degrees C. and gets progressively worse at lowertemperatures. The poor performance is encountered with both the directtemperature following and the power following control methods. The poorperformance can be explained in part by the difficulty in chilling thewater/methanol mixture below 0 degrees C., the relatively poor viscosityof the freezing water/methanol mixture, and the low temperaturedifference that results between the chilled water/methanol mixture andthe set point. The low temperature difference becomes a problem, inpart, because the system is unable to cool the DUT as quickly inresponse to self-heating, for example. This results in a greaterdeviation in the temperature of the DUT from the set point. This is tobe contrasted with the performance of HFE7100 which maintains a setpoint deviation of less than approximately 4 or 5 degrees C. throughoutthe entire range of set point temperatures from −10 degrees C. to +110degrees C.

The power dissipation through the heat exchanger heater increases withthe set point-to-liquid temperature difference. Flow metering throughthe heat sink is used to optimize the power dissipation wheneverpossible. Flow metering can also be used to reduce the load on the heatexchanger heater, enabling higher temperatures at lower powerdissipations. The limit to the flow metering is the heat-sink outlettemperature of the coolant, and any associated limits (e.g., exceedingthe boiling point of the liquid at the system pressure). Decreasing theflow rate can allow a greater temperature between the liquid and the setpoint by decreasing the amount of heat that is drawn away from theheater. The heater is thus able to heat the DUT to a higher temperature.A particular embodiment has a maximum flow rate of 4 liters/minute and aheater power of 300 watts.

An embodiment of the present invention also enables a fast transitionbetween different set points. Previous systems might require severalhours to change between two different set points. The present inventionenables this to be achieved in roughly 20-30 seconds between most setpoints. This reduction is due, in part, to the fact that the sameequipment can be used for all set points of interest and the same liquidcan be used in the heat sink chamber for all set points of interest.Further, the use of a heater along with a heat sink, and operating themat different temperatures, obviates the need for the heat sink liquid tomove between the actual set points. This may offer an advantage if theliquid need only be moved over a smaller temperature range than the setpoint.

However, embodiments of the present invention can also move between setpoint temperatures by changing only the temperature of the liquid andnot using the heater to effect the transition. Given that the sameliquid is used for both set point temperatures, the system can stillachieve the new set point temperature in a reduced time, as describedabove in the discussion on chillers.

Ideally, the control system will move the DUT temperature at the highestsafe thermal expansion rate of the DUT and then clip the temperature atthe set point. A linear, or trapezoidal, curve, with a slope indicativeof a safe expansion rate is often desired in temperature profiles. Thisis as opposed, for instance, to an asymptotic approach to the desiredtemperature.

FIG. 4 contains two curves which show the temperature increase of twodevices from approximately 20 degrees C. to at least 100 degrees C., forembodiments of the present invention. The flip chip moved from anambient temperature of 20 degrees C. to a set point of 100 degrees C. inroughly 1.5 seconds, and to a set point of 110 degrees C. in roughly 3.5seconds. The wire bond with heat spreader moved from an ambienttemperature of 20 degrees C. to a set point of 100 degrees C. in roughly4.5 seconds.

C. Delta T

The system's temperature control accuracy is partially dependent on thetemperature difference between the set point and the liquid. FIG. 8illustrates the temperature control accuracy of an HFE7100 based systemversus a water/methanol based system. The water/methanol system has anaccuracy fall-off at cold due to increasing viscosity inducingdecreasing flow rate through the heat exchanger. HFE7100 has moreconsistent flow and viscosity across the liquid coolant temperaturerange. Although the HFE7100 will boil at approximately 60° C., thehigher set point temperatures are achievable with the higher setpoint-to-liquid temperature differences. That is, the heater can add therequired heat.

A higher temperature difference also gives the heater more room tooperate in either overshooting or undershooting the desired set pointtemperature. If the temperature difference between the heat sink and theheater is low, then the heater may “bottom out” if it is desired tosharply reduce the heater power. Such a reduction may be needed, forexample, to offset self-heating of the device under test.

FIG. 9 illustrates that the junction temperature accuracy is as good orbetter with higher set point-to-liquid temperature differences. Withlarger temperature differences, the set point can be changed rapidlywith little impact on the achievable temperature control performance.The “Delta T” curve is created from the individual data pointsindicating the Delta T used at different set point temperatures. The“Extreme Deviation from Set Point” curve is created from the individualdata points indicating the maximum deviation that occurred at thedifferent set points. As can be seen from FIG. 9, as delta T isincreased from approximately 30 degrees C., corresponding to a set pointof approximately 30 degrees C., the deviation is relatively constant ordecreasing. Much of the variation in the Delta T curve of FIG. 9 iscaused by changes in the liquid temperature.

FIG. 12 also illustrates another example of maintaining the temperatureof the device under test (“DUT”) at successively higher delta T's. InFIG. 12, delta T is the difference between the “Fluid In T” line and the“Hx Temp.” line. The set points (not shown) are roughly 5, 30, and 70degrees C. The “Power to DUT” curve shows that the DUT is drawing avariable amount of power and therefore experiencing fluctuatingself-heating. The “HX Temp.” curve shows how the heater power, andtherefore temperature, is controlled to maintain the “DUT Temp.” curveclose to the desired set point. The “HX Temp.” curve, in conjunctionwith the “Fluid In T” curve, also show how the set point is moved twice,at roughly 22 seconds and 42 seconds, simply by changing the heaterpower and without changing the temperature of the liquid.

The delta T range is variable based on several parameters. Theseparameters include the flow rate through a given heat sink design, theheat sink design itself, the maximum power level of the heater, thegeometries of the heater and the DUT, and how much thermal load the DUTputs on the heater. In a typical application, 50 degree C. is a typicaldelta T value, but higher values are obtainable. Higher values can beobtained by adjusting the above, and other, parameters, such as bytrimming down the coolant flow rate.

D. Profiles

Referring to FIG. 1, the system controller 14 executes software whichinterfaces to an operator via the operator interface terminal 12. Thesoftware includes the Windows NT operating system, Labview programmingenvironment, and custom software developed to operate under Labview toperform the various functions of the system. A touch screen is used tosimplify operation, but the keyboard/mouse interface is supported aswell. A vocal input could also be used. It will be recognized that avariety of other software environments and user interfaces could beused.

The software allows for “profiles” to be defined and stored. Theprofiles specify the forcing temperature, rate of change to the newtemperature and how the profile is advanced. Typically, this can beeither time related, or advanced by signals from an external source,such as automatic test equipment used to test the chip. FIG. 5illustrates an example of the system software setup screens used toconstruct the profiles. The example profile indicates a sequence of nineset points for the DUT ranging from 70 degrees C. to 90 degrees C.,allowable deviation of +/−2 degrees C., a temperature of 40 degrees C.for the liquid in the heat sink, a Delta T of 20 degrees C., and athermal control mode of power following for each set point. The exampleprofile includes a variety of other fields related to soak time, PIDcontrol, data collection, and DUT temperature ramp control.

The profiles can be programmed to cause the heater to overshoot orundershoot the desired set point in order to change the temperature ofthe DUT more quickly. The profiles can also be programmed to achieve thetrapezoidal temperature curves described earlier.

The set point deviation can be characterized with a number of differentmethods. In many applications, the set point deviation is specified asbeing no greater than 3 degrees C. for power densities no greater than20 watts/cm², and as being no greater than 5 degrees C. for powerdensities no greater than 30 watts/cm². That is, the actual temperaturewill be within +/−3 degrees, or +/−5 degrees, of the set pointtemperature. The actual figure depends on a variety of factors,including without limitation, whether the die is exposed or encased, theactual power density, and the thermal resistance of the die-heaterboundary. In typical applications, the set point deviation is kept lowenough such that results of a test of the DUT which determines f_(max)at a set point temperature can be relied on as being accurate. The Jonesapplication (provisional application Ser. No. 60/092,720 mentioned abovehas a more detailed discussion of fmax and its importance as abenchmark. Typically, an entire curve is determined by calculatingf_(max) at a variety of different temperature values. The set pointdeviation should be kept sufficiently low at each of the differenttemperature values so that each is a reliable figure.

E. Test Control and Temperature Determination

As described in the disclosure, a control system maintains the DUTtemperature at a specified set point within a given tolerance. Thecontrol system must therefore have some information on the DUTtemperature. Some control systems, such as direct temperature following,require constant DUT temperature information. Other control systems,such as power following, which control deviation from a set point, donot need constant DUT temperature information but only need to know whento begin the temperature maintenance process.

The maintenance, or deviation control, process often begins after theDUT has reached the set point temperature. This information may bedetermined indirectly, for example, after a soak timer has expired. Itmay also be determined directly, for example, by monitoring a thermalstructure. Thermal structures can be used to supply initial DUTtemperature information and they can also be monitored throughout thetest if they are properly calibrated. One embodiment of the presentinvention monitors thermal structures to determine the initial DUTtemperature before initiating a power following temperature controlmethod.

Embodiments of the present invention may include separate controlsections to control the temperature and to control the test sequence.Referring to FIG. 13, there is shown a generic high-level block diagramillustrating a test control system 130 and temperature control system132, both of which are connected to and communicate with a DUT 134. Thisdisclosure has been primarily concerned with describing the temperaturecontrol system 132. The test control system 130 would operate theappropriate tests on the DUT 134 while the temperature control system132 controlled the DUT temperature.

These two control systems 130, 132 need to communicate or otherwisecoordinate their activities. Either the temperature control system 132or the test control system 130 can monitor a thermal structure. In oneembodiment of the present invention, the test control system 130monitors the thermal structure of the DUT 134 and sends a signal, suchas a scaled voltage, to the temperature control system 132 indicatingthe DUT temperature. FIG. 13 shows the communication path of such anembodiment with a dashed line between the test control system 130 andthe temperature control system 132. Embodiments of the control systemsand their architecture may vary considerably. In one embodiment, the twocontrol systems 130, 132 are separate and have no direct communication.Both control systems 130, 132 monitor the DUT 134 to gain the necessaryDUT temperature information in order to coordinate their activities. Ina second embodiment, the two control systems 130, 132 are fullyintegrated.

3. Examples

One present embodiment uses HFE7100 as the liquid coolant, operating inthe temperature range of −40° C. to +40° C. The temperature differencebetween the coolant supply and the chip set point temperature rangesbetween 5° C. and 160° C. The high temperature is limited by long termreliability issues associated with rapid, large, repeated temperaturevariations and associated thermal stresses of the coolant loop and theheater/heat exchanger assembly. It is also limited by the maximum setpoint to average liquid temperature difference sustainable with thepower rating of the heater power supply. It is also limited by thematerials and processes used to manufacture the heater/heat exchangerassembly, such as the breakdown temperature of an epoxy, the meltingpoint of a solder, or the boiling point of a coolant. The current systemcalls for a chip set point temperature range of −35° C. to +125° C. Thiswould require at least an 85 degree C. Delta T if the liquid coolant wasat 40 degrees C. In practice, however, a larger Delta T is desired sothat the heater can overshoot the desired temperature to achieve afaster response. One embodiment of the present invention uses anoperating delta T of between approximately 5 degrees C. andapproximately 100 degrees C.

A second embodiment uses water or a water/glycol (antifreeze) orwater/methanol mixture, operating in the temperature range of +10° C. to+90° C. The temperature difference between the liquid and the chip setpoint temperature can range between 5° C. and 160° C. The chip set pointtemperature ranges between +15° C. to +170° C.

Another embodiment has a chiller temperature range of −40 degrees C. to50 degrees C. The set point temperature is specified at 0 degrees C. to110 degrees C. It can use the heater for active control, to compensatefor self-heating of the DUT, from 40 degrees C. to 110 degrees C. Theperformance of the active control will degrade as the set pointtemperature approaches the coolant temperature. The amount of thedegradation depends on the package type and the power density, amongother things. Degradation is displayed in an increased die temperaturedeviation.

4. Variations

A heat exchanger may have many other implementations in addition to theembodiment described above. In particular, a heat exchanger need notinclude both a heater and a heat sink at the same time. Further, a heatexchanger may comprise, or even consist of, any device which eitherabsorbs and/or supplies heat. A heat exchanger may include multipleheaters, laid side by side or stacked one on top of another, dependingon the desired effect.

As one of ordinary skill in the relevant art will readily appreciate, inlight of the present and incorporated disclosures, the functions of theoverall system can be implemented with a variety of techniques. Inaccordance with an aspect of the present invention, the functionalitydisclosed herein can be implemented by hardware, software, and/or acombination of both.

Electrical circuits, using analog components, digital components, or acombination may be employed to implement the control, processing, andinterface functions. Software implementations can be written in anysuitable language, including without limitation high-level programminglanguages such as C++, mid-level and low-level languages, assemblylanguages, application-specific or device-specific languages, andgraphical languages such as Lab View. Such software can run on a generalpurpose computer such as a Pentium, an application specific piece ofhardware, or other suitable device. In addition to using discretehardware components in a logic circuit, the required logic may also beperformed by an application specific integrated circuit (“ASIC”) orother device.

The system will also include various hardware components which are wellknown in the art, such as connectors, cables, and the like. Moreover, atleast part of this functionality may be embodied in computer readablemedia (also referred to as computer program products), such as magnetic,magnetic-optical, and optical media, used in programming aninformation-processing apparatus to perform in accordance with theinvention. This functionality also may be embodied in computer readablemedia, or computer program products, such as a transmitted waveform tobe used in transmitting the information or functionality.

Further, the present disclosure should make it clear to one of ordinaryskill in the art that the present invention can be applied to a varietyof different fields, applications, industries, and technologies. Thepresent invention can be used with any system in which temperature musteither be monitored or controlled. This includes many differentprocesses and applications involved in semiconductor fabrication,testing, and operation. The temperature of interest may be that of anyphysical entity, including, without limitation, an electronic device orits environment, such as air molecules either in a flow or stationary.

The principles, preferred embodiments, and modes of operation of thepresent invention have been described in the foregoing specification.The invention is not to be construed as limited to the particular formsdisclosed, because these are regarded as illustrative rather thanrestrictive. Moreover, variations and changes may be made by those ofordinary skill in the art without departing from the spirit and scope ofthe invention.

We claim:
 1. An apparatus for controlling a temperature of asemiconductor device, the apparatus comprising: a heater, adapted to bethermally coupled to the semiconductor device; a heat sink thermallycoupled to the heater, wherein the heat sink defines a chamber and thechamber is adapted to have a liquid flowing through the chamber; and atemperature control system, coupled to both the heater and the heatsink, for controlling a temperature of a point on either the heater orthe semiconductor device; wherein the temperature control system isadapted to move the temperature of the point on the heater or the devicefrom approximately a first set point temperature to approximately asecond set point temperature by changing the control of the heater andmaintaining at a substantially constant temperature the liquid flowinginto the chamber, the liquid having an operative temperature range thatextends as low as approximately −40 degrees C., and the operative setpoint temperatures extending as low as approximately −10 degrees C. 2.The apparatus of claim 1, wherein the first set point temperature is atleast 25 degrees C. above the substantially constant temperature of theliquid flowing into the chamber.
 3. The apparatus of claim 1, whereinthe first set point temperature is below 35 degrees C. and the secondset point temperature is above 65 degrees C.
 4. The apparatus of claim3, wherein the temperature control system moves the temperature of thepoint on the heater from approximately the first set point temperatureto approximately the second set point temperature within five minutes.5. The apparatus of claim 1, wherein the heater is adapted to bethermally coupled to the semiconductor device while the semiconductordevice is in a socket.
 6. The apparatus of claim 1, wherein the heatercomprises a resistive heating element.
 7. The apparatus of claim 1,wherein the heater is adapted to be disposed below the semiconductordevice and adapted to be in thermally conductive contact with thesemiconductor device.
 8. The apparatus of claim 7, wherein the apparatusis adapted to force helium gas into a contact region between the heaterand the semiconductor device.
 9. The apparatus of claim 1, wherein thetemperature control system comprises an analog circuit.
 10. Theapparatus of claim 1, wherein the liquid which the chamber is adapted tohave flowing through the chamber comprises ethyl nonafluorobutyletherand ethyl nonafluoroisobutylether.
 11. The apparatus of claim 1, whereinthe temperature control system is adapted to receive an input related toa temperature of a point on the semiconductor device.
 12. The apparatusof claim 11, wherein the temperature control system is adapted tomaintain the temperature of the point on the semiconductor device atapproximately the first set point temperature despite potentialfluctuations in the semiconductor device temperature caused byself-heating.
 13. The apparatus of claim 11, wherein the temperaturecontrol system is adapted to maintain the temperature of thesemiconductor device at approximately a set point temperature which isat least 50 degrees C. above a temperature of the liquid flowing intothe heat sink.
 14. The apparatus of claim 11, wherein the input relatedto the temperature of the semiconductor device which the temperaturecontrol system is adapted to receive is selected from a group consistingof a power profile for the semiconductor device, power consumption ofthe semiconductor device, current consumption of the semiconductordevice, temperature of the semiconductor device, and a signal containinginformation from a thermal structure in the semiconductor device. 15.The apparatus of claim 12, wherein the temperature control system isadapted to control the temperature of the point on the semiconductordevice to within +/−20 degrees C. of the first set point temperaturedespite potential fluctuations in the semiconductor device temperaturecaused by self-heating.
 16. The apparatus of claim 12, wherein thetemperature control system is adapted to maintain the temperature of thepoint on the semiconductor device at approximately the first set pointtemperature despite potential fluctuations in the semiconductor devicetemperature caused by self-heating, such that results of a test of thesemiconductor device determining f_(max) at the first set pointtemperature can be relied on as being accurate.
 17. The apparatus ofclaim 14, wherein the temperature control system is adapted to maintainthe temperature of the point on the semiconductor device atapproximately the first set point temperature while the temperature ofthe liquid flowing into the chamber is maintained at approximately aconstant temperature which is at least 25 degrees C. below the first setpoint temperature.
 18. The apparatus of claim 1, wherein the apparatusis adapted to use a common liquid in the chamber of the heat sink forboth set point temperatures, and wherein the control of the heater isadapted to remain substantially constant while the temperature controlsystem moves the temperature of the liquid in the chamber.
 19. Theapparatus of claim 18, wherein: the temperature control system isadapted to receive an input related to the temperature of thesemiconductor device, and the temperature control system is adapted tomaintain the temperature of the semiconductor device at approximatelythe first set point.
 20. The apparatus of claim 18, wherein thetemperature control system is adapted to control the heater so as tomaintain the temperature of the semiconductor device at or near thefirst set point temperature, and at or near the second set pointtemperature, despite potential fluctuations in the semiconductor devicetemperature caused by self-heating.
 21. The apparatus of claim 20,wherein the first set point temperature is less than −25 degrees C. andthe second set point temperature is greater than 35 degrees C.
 22. Theapparatus of claim 1, wherein the temperature control system is adaptedto move the temperature of the point on the semiconductor device by atleast 50 degrees C. by controlling power sent to the heater and bycontrolling a temperature of a surface of the heat transfer unit. 23.The apparatus of claim 22, wherein: the temperature control system isadapted to control a temperature of the liquid flowing into the chamberand thereby to control the temperature of the surface of the heat sinkwhich contacts the incoming liquid.
 24. The apparatus of claim 1,wherein the temperature control system is adapted to maintain atemperature of a point on the semiconductor device at or near a setpoint temperature despite the existence of self-heating of thesemiconductor device and is adapted to provide the control of thetemperature of the point on the semiconductor device by changing atemperature of the heater and maintaining a temperature of a surface ofthe heat sink at an approximately constant temperature.